1. Field of the Invention
The disclosed invention relates to a memory device and a semiconductor device including the memory device.
Memory devices herein refer to general devices including memory elements, and are not limited to a main memory device and an auxiliary memory device. For example, an arithmetic device that includes a device including a memory element, such as a register, is regarded as a memory device.
Note that semiconductor devices herein refer to general elements and devices which function by utilizing semiconductor characteristics.
2. Description of the Related Art
A semiconductor device in which arithmetic processing is performed in a plurality of processors for high arithmetic capacity, what is called, a multiprocessor-system semiconductor device has become widespread. Multiprocessor-system-based semiconductor devices are classified into a loosely coupled system, a tightly coupled system, and the like in accordance with coupling systems of individual processors.
In a loosely coupled system, each processor has a special-purpose memory and can almost independently perform arithmetic processing. However, common data for a plurality of processors needs to be stored in each special-purpose memory of individual processors. Therefore, each processor needs a large-scale special-purpose memory.
In a tightly coupled system, a shared memory to which a plurality of processors has an access is provided, and individual processors can perform arithmetic processing with the use of common data stored in the shared memory. An example of a tightly coupled system is a multi-core processor in which a plurality of processor cores is provided for one processor package.
As a shared memory of such a tightly coupled system multiprocessor, a dual-port memory which has two input/output ports, or the like can be given (e.g., Patent Document 1).